bitmap picture character reverse

[scream2ice]

i'm writing a program that reverses the first 600 characters of a bitmap picture (it basically swaps character 0 with char 599, 1 with 598 and ......)
This is what i've written so far but it's not working

#include <iostream.h>
#include <fstream.h>
#include<conio.h>

int main()
{
	char c1,c2;
	int i,j;
	fstream pic;
	pic.open("mry.bmp", ios::in|ios::out| ios::binary);
	if(!pic)
	{
		cout<<"Error! "<<endl;
		return 1;
	}

	for( i=0,j=600; i<j; i++,j--)
	{
		pic.seekg(i);
		pic.get(c1);
		pic.seekg(j);
		pic.get(c2);
		pic.seekp(i);
		pic.put(c2);
		pic.seekp(j);
		pic.put(c1);
	}
getch();
return 0;
}

can anyone give me a clue on why it's not working and how it could be improved